The present invention relates to a system for controlling a fluid pressure, and more specifically to a pressure control system which is suitable for an anti-skid brake control and/or a traction control of a motor vehicle.
Similar fluid pressure control systems are disclosed in a pending U.S. patent application Ser. No. 07/645,415, filed on Jan. 24, 1991 in the name of Akira HIGASHIMATA et al. with a claim for priority based on a Japanese Patent Application No. 2-13672.
Japanese Patent (post examination) Publication No. 56-254 discloses a conventional anti-skid brake pressure control system. This system normally allows a fluid pressure to flow from a pressure source such as a master cylinder to a hydraulic actuator such as a wheel cylinder. When it becomes impossible to properly control the actuator with the fluid pressure of the pressure source, the control system interrupts the fluid communication between the pressure source and the actuator, and controls the fluid pressure supplied to the actuator, independently of the pressure of the pressure source, with a hydraulic modulator. This modulator uses a ball valve for disconnecting the wheel cylinder and the master cylinder, and a pneumatic diaphragm mechanism for operating the ball valve and modulating the fluid pressure of the wheel cylinder. In this conventional system, however, the pneumatic circuit including an air pump is complicated and expensive, and the use of the diaphragm makes it difficult to reduce the size of the system.